REE contents in solid sample media and stream water from different geological contexts: Comparison between Italy and Sweden
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Abstract Eight trenches were excavated to a depth of 4.6 m and filled with one of three different textures of spoil to evaluate topsoil and subsoil thickness requirements for crop production on nonsaline, nonsodic spoil material. Yields of wheat ( Triticum aestivum L.) in 1979 and 1982, barley ( Hordeum vulgare L.) in 1980, and corn ( Zea mays L.) in 1981 and 1983 were compared on plots with 0.23, 0.46, or 0.69 m of topsoil replaced over loamy sand spoil with and without subsoil, over clay loam spoil, or over silty clay loam spoil. Crop yields increased with increasing thickness of replaced topsoil, especially on trenches filled with loamy sand spoil. Crop yields were greater when subsoil was replaced than when no subsoil was replaced on loamy sand spoil at a given topsoil thickness. Average yields from the trenches were equal to or better than average yields from undisturbed plots in 1979 and 1983. On irrigated plots in 1983, response of silage and corn grain to subsoil/spoil treatments was similar to the nonirrigated plots. Wheat grown on irrigated plots in 1982 did not respond significantly to topsoil thickness or subsoil/spoil treatments. At least 0.69 m of topsoil plus subsoil was required to achieve highest yields on nonsodic, nonsaline, loamy sand spoil, but 0.46 to 0.69 m of topsoil was sufficient for highest yields on clay loam and silty clay loam nonsaline, nonsodic spoil. Crop yields were not increased by broadcast applications of N and P fertilizer.
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Topsoil application along roadsides results in added expense, delays seeding newly constructed areas, and creates potential erosion sites when moisture and seedbed conditions may be optimum for germination and plant growth. Two experiments were conducted to compare establishment of vegetation on graded highway cuts. One was concluded on Groseclose subsoil near Blacksburg, Virginia, comparing surface application on NPK fertilizer and lime (L) on smooth (glazed) subsoil, on tilled subsoil before NPKL application, on tilled subsoil after NPKL application, and with surface application of NPKL to 15 cm of topsoil. Experiment 2 was conducted on Lenoir subsoil near Gloucester to compare a 15-cm layer of tilled topsoil to tilled subsoil, and smooth top soil to glazed subsoil. Each area was fertilized with NPK at rates of 168-146-139, 112-98-93, and 84-73-70 (kg/ha). Incorporated NPKL and roughened subsoils gave 8 and 11% better vegetative cover (about 0.3 more crownvetch (Coronilla varia L.) plants/dm2) than did 15 cm of topsoil over subsoil. Tilled topsoil or subsoil had about a fourfold better vegetative cover than when either was left smooth. Erosion was 50 and 25% as great on tilled topsoil and subsoil, respectively, than on either left smooth. Bulk density of smooth and roughened topsoil or subsoil ranged from 1.38 to 1.42 g/cm3 as compared to 1.76 g/cm3 for the compacted smooth subsoil. Likewise, total porosity was increased from 22 to 42% above glazed subsoil by roughening and use of topsoil. The altered physical properties created by roughening increased plant growth by increasing soil moisture content of the topsoil by 23% and that of the topsoil by 45% and by decreasing soil temperature. Tilled subsoils with adequate soil amendments can result in satisfactory plant covers similar to those obtained by topsoiling at a much lower cost.
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Abstract The study involved the liming of two acid soils, one high in extractable Al and one of similar pH, but low in extractable Al. Portions of each soil were treated in the laboratory with Ca(OH) 2 (labeled with Ca 45 ) to bring the pH to three levels. One of the soils also had been maintained in the field at the same pH levels for many years. Three depths of topsoil were used with corresponding depths of subsoil. These soils were placed in 18‐inch cylinders and cropped to alfalfa. Results indicated that plant yields, root proliferation, and consequent uptake of Ca depend largely on adequate level of lime in both topsoil and subsoil. However, if sufficient lime was applied to the topsoil, near maximum yields were obtained regardless of the lime level of the subsoil. Subsoil liming had minor effects on yield and uptake of Ca except when the topsoil was shallow and more acid. The soil with the highest level of Al responded proportionally more to the lime added. Freshly added Ca appeared to be more available to alfalfa than Ca added earlier in the field. The percentage of Ca from the topsoil‐applied source increased from 8 to 100% as the rate of liming increased from ½ to 8 tons per acre in a 3‐inch layer of the most acid soil. With increased level of lime in the subsoil, smaller percentages came from the Ca applied to the topsoil. Root growth generally reflected what yields and Ca uptake had indicated. Root cation‐exchange capacities increased with increased rate of liming.
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Abstract The interacting effects between topsoil water supply, nitrogen (N) placement and subsoil aluminum (Al) toxicity on wheat growth were studied in two split‐root pot experiments. The native nitrate‐N (NO3‐N) in the topsoil used in each experiment differed and were designated as high (3706 μM) and low (687 μM) for experiments one and two, respectively. Wheat was grown in pots that enabled the root system to be split so that half of the roots were in topsoil and the other half were in subsoils containing varying concentrations of soluble Al. Treatments were imposed which varied the supply of water to the topsoil (either ‘wet’ or ‘dry'). Placement of applied N in either the topsoil or subsoil had little effect on either shoot or root fresh weight, or on the length of roots produced in the subsoil section of the split pots. When water supply to the topsoil was decreased, both shoot and root growth of wheat declined and the yield decrease increased with subsoil Al. In the high‐N experiment, wheat grown in the low Al subsoil with the high native soluble subsoil (NO3 (3002 μM) was able to exploit the N and subsoil water, hence both shoot and root growth increased considerably in comparison to shoot and root growth of wheat grown in soils containing higher concentrations of subsoil Al. When the native NO3 was lower (i.e. the low‐N experiment) inadequate root proliferation restricted the ability of plants to use subsoil N and water irrespective of subsoil Al. The results from this study suggest that wheat, grown on yellow earths with Al‐toxic subsoils, will suffer yield reductions when the topsoil dries out (e.g. in the spring when winter rainfall ceases) because subsoil reserves of water and nitrogen are under utilised.
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Abstract Numerous factors affect the composition and quality of crops. One of these factors is soil thickness, which can affect quantity of nutrients available, availability of water, and rooting depth. This experiment was conducted in North Dakota to determine the effects of variable thicknesses of topsoil and subsoil over sodic mine spoils on nitrogen (N) and phosphorus (P) concentrations in blue grama and side oats grama ( Bouteloua gracilis and Bouteloua curtipendula ), crested wheatgrass ( Agropyron desertorum ), alfalfa ( Medicago sativa ), and hard red spring wheat ( Triticum aestivum ). Milling and baking qualities of spring wheat were also evaluated. Total phosphorus concentration in most crops was not consistently affected by subsoil thickness; however, total P in plant material was usually greatest when subsoil was covered with either 20 or 60 cm of topsoil. Mixing subsoil and topsoil in a 3:1 ratio frequently gave plant P concentrations almost as low as for treatments of no topsoil over subsoil. A notable exception was alfalfa. Plant nitrogen concentration tended to decrease as subsoil thickness increased. Much of this decrease may have resulted from simple dilution, since total plant growth generally increased as total soil thickness increased to 90 to 120 cm. Except for alfalfa, N concentration was greater in all crops produced on 20 to 60 cm of topsoil over subsoil than on plots with no topsoil or subsoil and topsoil mixed. Generally, milling and baking properties of the wheat grain were closely related to the grain N concentration. Based on several parameters of milling and baking quality, flour from wheat produced on plots with 20 or 60 cm of topsoil generally was superior in milling and baking properties to flour from wheat on plots with no topsoil or with subsoil and topsoil mixed. In general, presence of topsoil affected crop quality by enhancing nutrient uptake by the plant. On the other hand, increased subsoil thickness often increased rooting depth and water availability, resulting in increased plant growth and, consequently, dilution of nutrient concentrations in the crops produced.
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